In recent years, electronic parts are becoming small sized and thin, and it is an important technical task to relax a stress with regard to a material applied to these parts. For example, with regard to a material which is directly coating the electronic parts, a high stress relaxing property is required. In particular, whereas the size of the whole parts is becoming small, a chip mounted thereon is becoming a large sized and thin so that a damage caused by the stress at the time of curing or after curing is likely caused. Under these background situations, the resin itself is required to have less stress. In particular, for forming a product in which a plural number of bear chips are mounted on the same substrate like an IC card or a resin dam of a lead frame, a slight residual stress at the time of curing becomes a cause of breakage of wiring, warpage of a substrate or distortion of a frame.
For forming a product on which a plural number of bear chips are mounted on the same substrate like an IC chip or a resin dam of a lead frame, an epoxy resin, etc., has conventionally been used, but the resin has a large stress accompanied by shrinkage at curing so that breakage of wiring or occurrence of crack after curing becomes problems in a heat cycle test after curing or a solder reflow test. Also, with regard to strain at the time of forming a resin dam on a lead frame, a mold resin is flown out from the portion at which strain occurs whereby there is a problem of molding failure at molding.
To solve these problems, an attempt has been made in Japanese Provisional Patent Publication No. 311520/1990 by adding a silicone rubber elastic material to an epoxy resin composition where by providing a flexibility and relaxing stress. However, there are problems that adhesiveness is lowered or resin strength is lowered.
Also, in CSP (chip size package), a solder connecting portion is plastically deformed in a semiconductor device in a surface mounting type such as a bear chip packaging, by a stress caused by the difference of thermal expansion coefficients between a semiconductor element and a substrate, and when this is repeated, the device is broken by fatigue. Thus, it has been carried out a device to reduce a stress caused by the difference in the thermal expansion coefficient of a substrate by providing an inter poser or a stress relaxing layer between the semiconductor element and the substrate. For example, in a semiconductor device shown in Japanese Provisional Patent Publication No. 79362/1998, stress is relaxed by making a bump high. Also, for the purpose of ensuring high reliability of a package in a heat cycle test or a solder reflow test, etc., a stress relaxing layer or an adhesive layer comprising a low elasticity material to relax the difference of the thermal expansion coefficients of a silicon chip and a substrate has been used. Moreover, in a bear chip practical packaging, there is no structure at the inside of the semiconductor to relax the stress so that a device to reduce the stress caused by the difference of the thermal expansion coefficients of the substrate has been carried out by providing an underfill resin layer between the semiconductor element and the substrate.
However, in the structure of relaxing a stress at the connecting portion by the height of the bump as mentioned above, the stress is rather concentrated to the bump itself so that there is a problem of causing connection failure. Also, in the method of using the underfill resin layer in combination, a resin is required to fill in a narrow gap between the semiconductor device and the substrate so that a filling operation is troublesome. Moreover, it is difficult to fill the resin uniformly in the whole portion of the gap so that there is a problem of lowering in production efficiency of the semiconductor device.
In μBGA (ball grid array) which is one example of CSP, a low elastic material has been used for the purpose of ensuring connection reliability between a lead from a “TAB” (tape automated bonding) tape and an electrode on a silicon chip, and adhering the TAB tape and the silicon chip.
Moreover, as a technique of integrating a wafer process and a package process which had been completely separated, a wafer level CSP process in which a package is prepared in a wafer state with the same size as the chip size has been proposed. According to this process, not only the production cost of the package can be reduced but also wire length can be shortened so that there are merits that a signal delay or noise in the package can be reduced and high speed moving can be realized.
In this package, to ensure high reliability, it is necessary to use a stress relaxing layer or an adhesive layer comprising a low elastic material to relax the difference of the thermal expansion coefficients between the silicon chip and the substrate as in the conventional CSP such as μBGA.
In the wafer level CSP process, to connect an electrode of the chip to an outer practically mounting substrate, a metal layer which is so-called a re-wiring layer is formed on a stress relaxing layer by the sputtering method or the plating method, so that it is required not only to be low elasticity but also to have resistances to sputtering or plating.
However, the low elasticity material used in μBGA is low elasticity but is poor in heat resistance so that it has low resistance to sputtering or plating whereby it cannot be applied to the wafer level CSP process as such.
On the other hand, it has been carried out an attempt to relax the stress by adding a monomer component having rubber elasticity to an epoxy resin to lower the elasticity (Japanese Provisional Patent Publication No. 48544/1986), but by using these components in combination, there is a problem of lowering heat resistance of the resin.
A thermoplastic resin having high heat resistance generally has high resin elasticity and mechanical strength but is brittle so that it is applied to electronic parts as such, there are high possibility of causing inconveniences such as occurrences of warpage of a substrate after curing or resin crack in a thermal shock test. Thus, in Japanese Provisional Patent Publication No. 123824/1989, a method of copolymerizing a monomer component having rubber elasticity in a resin has been proposed. However, this method becomes a cause of lowering heat resistance of the resin itself so that it is not preferred.
In recent years, a polyimide, polyamide imide or polyamide resin, etc. excellent in heat resistance and mechanical resistance have widely been used in the field of electronics for a surface protective film or an interlayer insulating film of a semiconductor element. Recently, as a producing method of these surface protective film or interlayer insulating film, screen printing or dispense coating has been attracted attention. Also, as a method of forming a heat-resistant resin on a substrate such as chip, etc., spin coating method, screen printing method, dispense method, film laminate method, etc., have been known.
A material which realizes screen printing, there may be mentioned a material in which a filler is dispersed in a varnish such as a heat-resistant polyimide resin, etc., as a binder to make a paste. The filler of this material provide an effect of giving thixotropic property to the paste. As the filler, there is a method of using silica fine particles or heat-resistant insoluble polyimide fine particles. However, these materials involve the problem that many voids or bubbles are remained at the filler interface at heating and drying so that film strength is weak. To solve these problems, a heat-resistant resin paste as disclosed in Japanese Provisional Patent Publication No. 289646/1990 has been developed. This is a paste in which a filler of a polyamic acid is dispersed in a binder of a polyamic acid, and at the time of heating and drying, the filler is firstly dissolved and then, compatibilized with the binder and forms a uniform coating film at the time of film formation. However, it requires imidation step so that curing conditions of 300° C. or higher are required. Also, there are problems that elasticity is high and flexibility is poor. Moreover, in the other polyimide paste, similar problems are involved.
In the spin coating method, there are problems in environmental point and cost that a coating efficiency of the heat-resistant resin solution is generally 10% or less (90% or more are lost without coating to the substrate), etc. On the other hand, the screen printing method using a metal plate or a mesh plate has merits in the points that a heat-resistant resin can be coated only the required parts within a short period of time effectively. Also, the dispense method has merits that a heat-resistant resin can be coated only the required parts without contacting the material to be coated within a short period of time effectively.
As a heat-resistant resin paste which is capable of applying to coating systems excellent in coating efficiency such as the screen printing or the dispense, it has been reported in Japanese Provisional Patent Publication No. 142252/1997 a heat-resistant resin paste capable of forming a thick film pattern by using a heat-resistant resin paste which dissolves in a solvent at the time of heating and drying.
However, this heat-resistant resin has large elasticity so that there is a problem that it cannot be used as such as a stress relaxing material for relaxing the difference in thermal expansion coefficients of a silicon chip and the substrate.
On the other hand, accompanying with the request of making an electronic apparatus with a low cost, it has earnestly been desired to obtain a semiconductor device which realizes the same reliability with the conventional CSP and further the cost is reduced. To cope with the low cost material, it has been proposed a so-called wafer level CSP that is to obtain respective semiconductor devices by forming semiconductor devices together on a semiconductor wafer and then the wafer is cut. The reason why the cost of the method can be reduced is that the packaging step can be carried out on the wafer together so that a number of steps can be reduced as compared with the conventional CSP in which each semiconductor element cut from the wafer is treated, respectively. More specifically, as disclosed in Japanese Provisional Patent Publication No. 79362/1998, a Cu post is formed by an electroplating on a semiconductor wafer, and after encapsulating with a resin, the resin is polished until the top end portion of the Cu post is exposed, and a solder ball is mounted on the exposed Cu post top end portion and the semiconductor wafer is cut to the respective semiconductor devices.
However, in the preparation method of a wafer level CSP conventionally been proposed, a specific mold is required in many cases in the method of using an encapsulating resin. Also, in the method of using a spin coating step when an insulating layer is formed on the wafer surface, there is much loss in a material to be used, and there is a problem that a cost becomes much expensive until a mass production technique is established.
An object of the present invention is to provide a resin composition which can solve the above-mentioned problems, and gives a film having high strength and low elasticity, and excellent in flexibility only by a step of drying a solvent at 250° C. or lower, or by a step of drying a solvent at 250° C. or lower without imidation step.
Also, another object of the present invention is to provide a resin composition capable of forming a precise pattern by screening printing, dispense coating, etc. by giving thixotropic property of the resin composition with an aromatic thermoplastic resin which is insoluble in a polar solvent at room temperature but soluble by heating.
Another object of the present invention is to provide a resin composition capable of obtaining a coated film having the same resin characteristics as the polyimide only by a step of drying a solvent at 250° C. or lower, or by a step of drying a solvent at 250° C. or lower without imidation step, and giving a coated film having high strength and excellent flexibility, and a semiconductor device using the same.
Further object of the present invention is to provide a heat-resistant resin paste which is capable of widely utilizing for a coating material, an adhesive, a stress relaxing material of a semiconductor device, etc., of controlling elasticity optionally and of forming a resin film excellent in heat resistance, has thixotropic property and can be applied to coating systems excellent in coating efficiency such as screen printing and dispense coating, etc.
Still further object of the present invention is to provide a resin for insulating a semiconductor device to be used for a resin layer having high connection reliability by preventing line breakage at the metal wiring or solder connecting portion caused by thermal stress of a semiconductor device having a resin layer, and a semiconductor device using the resin for the resin layer.
Still further object of the present invention is to provide a method of producing a semiconductor device which controls loss of a material at the minimum amount, prevents connection failure and excellent in reliability, and a semiconductor device.